Cement set activators for set-delayed cement compositions and associated methods

ABSTRACT

Disclosed herein are cement compositions and methods of using set-delayed cement compositions in subterranean formations. In one embodiment, a method of cementing in a subterranean formation is described. The method may comprise providing a set-delayed cement composition comprising water, pumice, hydrated lime, and a set retarder; activating the set-delayed cement composition with a liquid additive to produce an activated cement composition, wherein the liquid additive comprises a monovalent salt, a polyphosphate, a dispersant, and water; and allowing the activated cement composition to set.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication No. 61/875,233, filed on Sep. 9, 2013, titled “Cement SetActivators for Set-Delayed Cement Compositions and Associated Methods”and is a continuation-in-part of U.S. patent application Ser. No.13/854,115, entitled “Cement Set Activators for Set-Delayed CementCompositions and Associated Methods,” filed on Mar. 31, 2013, which is acontinuation-in-part of U.S. patent application Ser. No. 13/417,001,entitled “Set-Delayed Cement Compositions Comprising Pumice andAssociated Methods,” filed on Mar. 9, 2012, the entire disclosures ofwhich are incorporated herein by reference.

BACKGROUND

Embodiments relate to subterranean cementing operations and, in certainembodiments, to set-delayed cement compositions and methods of usingset-delayed cement compositions in subterranean formations.

Cement compositions may be used in a variety of subterranean operations.For example, in subterranean well construction, a pipe string (e.g.,casing, liners, expandable tubulars, etc.) may be run into a wellboreand cemented in place. The process of cementing the pipe string in placeis commonly referred to as “primary cementing.” In a typical primarycementing method, a cement composition may be pumped into an annulusbetween the walls of the wellbore and the exterior surface of the pipestring disposed therein. The cement composition may set in the annularspace, thereby forming an annular sheath of hardened, substantiallyimpermeable cement (i.e., a cement sheath) that may support and positionthe pipe string in the wellbore and may bond the exterior surface of thepipe string to the subterranean formation. Among other things, thecement sheath surrounding the pipe string functions to prevent themigration of fluids in the annulus, as well as protecting the pipestring from corrosion. Cement compositions also may be used in remedialcementing methods, for example, to seal cracks or holes in pipe stringsor cement sheaths, to seal highly permeable formation zones orfractures, to place a cement plug, and the like.

A broad variety of cement compositions have been used in subterraneancementing operations. In some instances, set-delayed cement compositionshave been used. Set-delayed cement compositions are characterized byremaining in a pumpable fluid state for at least about one day (e.g., atleast about 7 days, about 2 weeks, about 2 years or more) at roomtemperature (e.g., about 80° F.) in quiescent storage. When desired foruse, the set-delayed cement compositions should be capable of beingactivated whereby reasonable compressive strengths are developed. Forexample, a cement set accelerator may be added to a set-delayed cementcomposition whereby the composition sets into a hardened mass. Amongother things, the set-delayed cement composition may be suitable for usein wellbore applications, for example, where it is desired to preparethe cement composition in advance. This may allow, for example, thecement composition to be stored prior to its use. In addition, this mayallow, for example, the cement composition to be prepared at aconvenient location and then transported to the job site. Accordingly,capital expenditures may be reduced due to a reduction in the need foron-site bulk storage and mixing equipment. This may be particularlyuseful for offshore cementing operations where space onboard the vesselsmay be limited.

While set-delayed cement compositions have been developed heretofore,challenges exist with their successful use in subterranean cementingoperations. For example, set-delayed cement compositions prepared withPortland cement may have undesired gelation issues which can limit theiruse and effectiveness in cementing operations. Other set-delayedcompositions that have been developed, for example, those comprisinghydrated lime and quartz, may be effective in some operations but mayhave limited use at lower temperatures as they may not developsufficient compressive strength when used in subterranean formationshaving lower bottom hole static temperatures.

BRIEF DESCRIPTION OF THE DRAWINGS

These drawings illustrate certain aspects of some of the embodiments ofthe present method, and should not be used to limit or define themethod.

FIG. 1 illustrates a system for the preparation and delivery of aset-delayed cement composition to a wellbore in accordance with certainembodiments.

FIG. 2A illustrates surface equipment that may be used in the placementof a set-delayed cement composition in a wellbore in accordance withcertain embodiments.

FIG. 2B illustrates the placement of a set-delayed cement compositioninto a wellbore annulus in accordance with certain embodiments.

FIG. 3 is a graph of the dispersant amount vs. the thickening time ofset-delayed cement compositions activated with a liquid additivecomprising a monovalent salt and polyphosphate activator combination.

DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments relate to subterranean cementing operations and, in certainembodiments, to set-delayed cement compositions and methods of usingset-delayed cement compositions in subterranean formations. Inparticular embodiments, improved cement set activators used for theactivation of set-delayed cement compositions may be provided.Embodiments of the cement set activators may be used to activate aset-delayed cement composition while also achieving desirable thickeningtimes and compressive strength development.

Embodiments of the set-delayed cement compositions may generallycomprise water, pumice, hydrated lime, and a set retarder. Optionally,the set-delayed cement compositions may further comprise a dispersant.Embodiments of the set-delayed cement compositions may be foamed.Advantageously, embodiments of the set-delayed cement compositions maybe capable of remaining in a pumpable fluid state for an extended periodof time. For example, the set-delayed cement compositions may remain ina pumpable fluid state for at least about 1 day, about 2 weeks, about 2years, or longer. Advantageously, the set-delayed cement compositionsmay develop reasonable compressive strengths after activation atrelatively low temperatures. While the set-delayed cement compositionsmay be suitable for a number of subterranean cementing operations, theymay be particularly suitable for use in subterranean formations havingrelatively low bottom hole static temperatures, e.g., temperatures lessthan about 200° F. or ranging from about 100° F. to about 200° F. Inalternative embodiments, the set-delayed cement compositions may be usedin subterranean formations having bottom hole static temperatures up to450° F. or higher.

The water used in embodiments of the set-delayed cement compositions maybe from any source provided that it does not contain an excess ofcompounds that may undesirably affect other components in theset-delayed cement compositions. For example, a set-delayed cementcomposition may comprise fresh water or salt water. Salt water generallymay include one or more dissolved salts therein and may be saturated orunsaturated as desired for a particular application. Seawater or brinesmay be suitable for use in embodiments. Further, the water may bepresent in an amount sufficient to form a pumpable slurry. In certainembodiments, the water may be present in the set-delayed cementcomposition in an amount in the range of from about 33% to about 200% byweight of the pumice. In certain embodiments, the water may be presentin the set-delayed cement compositions in an amount in the range of fromabout 35% to about 70% by weight of the pumice. One of ordinary skill inthe art with the benefit of this disclosure will recognize theappropriate amount of water for a chosen application.

Embodiments of the set-delayed cement compositions may comprise pumice.Generally, pumice is a volcanic rock that can exhibit cementitiousproperties in that it may set and harden in the presence of hydratedlime and water. The pumice may also be ground. Generally, the pumice mayhave any particle size distribution as desired for a particularapplication. In certain embodiments, the pumice may have a mean particlesize in a range of from about 1 micron to about 200 microns. The meanparticle size corresponds to d50 values as measured by particle sizeanalyzers such as those manufactured by Malvern Instruments,Worcestershire, United Kingdom. In specific embodiments, the pumice mayhave a mean particle size in a range of from about 1 micron to about 200microns, from about 5 microns to about 100 microns, or from about 10microns to about 50 microns. In one particular embodiment, the pumicemay have a mean particle size of less than about 15 microns. An exampleof a suitable pumice is available from Hess Pumice Products, Inc.,Malad, Id., as DS-325 lightweight aggregate, having a particle size ofless than about 15 microns. It should be appreciated that particle sizestoo small may have mixability problems while particle sizes too largemay not be effectively suspended in the compositions. One of ordinaryskill in the art, with the benefit of this disclosure, should be able toselect a particle size for the pumice suitable for a chosen application.

Embodiments of the set-delayed cement compositions may comprise hydratedlime. As used herein, the term “hydrated lime” will be understood tomean calcium hydroxide. In some embodiments, the hydrated lime may beprovided as quicklime (calcium oxide) which hydrates when mixed withwater to form the hydrated lime. The hydrated lime may be included inembodiments of the set-delayed cement compositions, for example, to forma hydraulic composition with the pumice. For example, the hydrated limemay be included in a pumice-to-hydrated-lime weight ratio of about 10:1to about 1:1 or 3:1 to about 5:1. Where present, the hydrated lime maybe included in the set-delayed cement compositions in an amount in therange of from about 10% to about 100% by weight of the pumice, forexample. In some embodiments, the hydrated lime may be present in anamount ranging between any of and/or including any of about 10%, about20%, about 40%, about 60%, about 80%, or about 100% by weight of thepumice. In some embodiments, the cementitious components present in theset-delayed cement composition may consist essentially of the pumice andthe hydrated lime. For example, the cementitious components mayprimarily comprise the pumice and the hydrated lime without anyadditional components (e.g., Portland cement, fly ash, slag cement) thathydraulically set in the presence of water. One of ordinary skill in theart, with the benefit of this disclosure, will recognize the appropriateamount of the hydrated lime to include for a chosen application.

Embodiments of the set-delayed cement compositions may comprise a setretarder. A broad variety of set retarders may be suitable for use inthe set-delayed cement compositions. For example, the set retarder maycomprise phosphonic acids, such as ethylenediamine tetra(methylenephosphonic acid), diethylenetriamine penta(methylene phosphonic acid),etc.; lignosulfonates, such as sodium lignosulfonate, calciumlignosulfonate, etc.; salts such as stannous sulfate, lead acetate,monobasic calcium phosphate, organic acids, such as citric acid,tartaric acid, etc.; cellulose derivatives such as hydroxyl ethylcellulose (HEC) and carboxymethyl hydroxyethyl cellulose (CMHEC);synthetic co- or ter-polymers comprising sulfonate and carboxylic acidgroups such as sulfonate-functionalized acrylamide-acrylic acidco-polymers; borate compounds such as alkali borates, sodium metaborate,sodium tetraborate, potassium pentaborate; derivatives thereof, ormixtures thereof. Examples of suitable set retarders include, amongothers, phosphonic acid derivatives. One example of a suitable setretarder is Micro Matrix® cement retarder, available from HalliburtonEnergy Services, Inc. Generally, the set retarder may be present in theset-delayed cement compositions in an amount sufficient to delay thesetting for a desired time. In some embodiments, the set retarder may bepresent in the set-delayed cement compositions in an amount in the rangeof from about 0.01% to about 10% by weight of the pumice. In specificembodiments, the set retarder may be present in an amount rangingbetween any of and/or including any of about 0.01%, about 0.1%, about1%, about 2%, about 4%, about 6%, about 8%, or about 10% by weight ofthe pumice. One of ordinary skill in the art, with the benefit of thisdisclosure, will recognize the appropriate amount of the set retarder toinclude for a chosen application.

As previously mentioned, embodiments of the set-delayed cementcompositions may optionally comprise a dispersant. Examples of suitabledispersants include, without limitation, sulfonated-formaldehyde-baseddispersants (e.g., sulfonated acetone formaldehyde condensate), examplesof which may include Daxad® 19 dispersant available from Geo SpecialtyChemicals, Ambler, Pa. Other suitable dispersants may bepolycarboxylated ether dispersants such as Liquiment® 5581F andLiquiment® 514L dispersants available from BASF Corporation Houston,Tex.; or Ethacryl™ G dispersant available from Coatex, Genay, France. Anadditional example of a suitable commercially available dispersant isCFR™-3 dispersant, available from Halliburton Energy Services, Inc,Houston, Tex. The Liquiment® 514L dispersant may comprise 36% by weightof the polycarboxylated ether in water. While a variety of dispersantsmay be used in accordance with embodiments, polycarboxylated etherdispersants may be particularly suitable for use in some embodiments.Without being limited by theory, it is believed that polycarboxylatedether dispersants may synergistically interact with other components ofthe set-delayed cement composition. For example, it is believed that thepolycarboxylated ether dispersants may react with certain set retarders(e.g., phosphonic acid derivatives) resulting in formation of a gel thatsuspends the pumice and hydrated lime in the composition for an extendedperiod of time.

In some embodiments, the dispersant may be included in the set-delayedcement compositions in an amount in the range of from about 0.01% toabout 5% by weight of the pumice. In specific embodiments, thedispersant may be present in an amount ranging between any of and/orincluding any of about 0.01%, about 0.1%, about 0.5%, about 1%, about2%, about 3%, about 4%, or about 5% by weight of the pumice. One ofordinary skill in the art, with the benefit of this disclosure, willrecognize the appropriate amount of the dispersant to include for achosen application.

Other additives suitable for use in subterranean cementing operationsalso may be included in embodiments of the set-delayed cementcompositions. Examples of such additives include, but are not limitedto: weighting agents, lightweight additives, gas-generating additives,mechanical-property-enhancing additives, lost-circulation materials,filtration-control additives, fluid-loss-control additives, defoamingagents, foaming agents, thixotropic additives, and combinations thereof.In embodiments, one or more of these additives may be added to theset-delayed cement compositions after storing but prior to the placementof a set-delayed cement composition into a subterranean formation. Aperson having ordinary skill in the art, with the benefit of thisdisclosure, should readily be able to determine the type and amount ofadditive useful for a particular application and desired result.

Those of ordinary skill in the art will appreciate that embodiments ofthe set-delayed cement compositions generally should have a densitysuitable for a particular application. By way of example, theset-delayed cement compositions may have a density in the range of fromabout 4 pounds per gallon (“lb/gal”) to about 20 lb/gal. In certainembodiments, the set-delayed cement compositions may have a density inthe range of from about 8 lb/gal to about 17 lb/gal. Embodiments of theset-delayed cement compositions may be foamed or unfoamed or maycomprise other means to reduce their densities, such as hollowmicrospheres, low-density elastic beads, or other density-reducingadditives known in the art. In embodiments, the density may be reducedafter storing the composition, but prior to placement in a subterraneanformation. Those of ordinary skill in the art, with the benefit of thisdisclosure, will recognize the appropriate density for a particularapplication.

As previously mentioned, the set-delayed cement compositions may have adelayed set in that they remain in a pumpable fluid state for at leastone day (e.g., at least about 1 day, about 2 weeks, about 2 years ormore) at room temperature (e.g., about 80° F.) in quiescent storage. Forexample, the set-delayed cement compositions may remain in a pumpablefluid state for a period of time from about 1 day to about 7 days ormore. In some embodiments, the set-delayed cement compositions mayremain in a pumpable fluid state for at least about 1 day, about 7 days,about 10 days, about 20 days, about 30 days, about 40 days, about 50days, about 60 days, or longer. A fluid is considered to be in apumpable fluid state where the fluid has a consistency of less than 70Bearden units of consistency (“Bc”), as measured on a pressurizedconsistometer in accordance with the procedure for determining cementthickening times set forth in API RP Practice 10B-2, RecommendedPractice for Testing Well Cements, First Edition, July 2005.

When desired for use, embodiments of the set-delayed cement compositionsmay be activated (e.g., by combination with an activator) to set into ahardened mass. The term “cement set activator” or “activator”, as usedherein, refers to an additive that activates a set-delayed or heavilyretarded cement composition and may also accelerate the setting of theset-delayed, heavily retarded, or other cement composition. By way ofexample, embodiments of the set-delayed cement compositions may beactivated to form a hardened mass in a time period in the range of fromabout 1 hour to about 12 hours. For example, embodiments of theset-delayed cement compositions may set to form a hardened mass in atime period ranging between any of and/or including any of about 1 day,about 2 days, about 4 days, about 6 days, about 8 days, about 10 days,or about 12 days.

In some embodiments, the set-delayed cement compositions may set to havea desirable compressive strength after activation. Compressive strengthis generally the capacity of a material or structure to withstandaxially directed pushing forces. The compressive strength may bemeasured at a specified time after the set-delayed cement compositionhas been activated and the resultant composition is maintained underspecified temperature and pressure conditions. Compressive strength canbe measured by either destructive or non-destructive methods. Thedestructive method physically tests the strength of treatment fluidsamples at various points in time by crushing the samples in acompression-testing machine. The compressive strength is calculated fromthe failure load divided by the cross-sectional area resisting the loadand is reported in units of pound-force per square inch (psi).Non-destructive methods may employ a UCA™ ultrasonic cement analyzer,available from Fann Instrument Company, Houston, Tex. Compressivestrength values may be determined in accordance with API RP 10B-2,Recommended Practice for Testing Well Cements, First Edition, July 2005.

By way of example, the set-delayed cement compositions may develop a24-hour compressive strength in the range of from about 50 psi to about5000 psi, alternatively, from about 100 psi to about 4500 psi, oralternatively from about 500 psi to about 4000 psi. In some embodiments,the set-delayed cement compositions may develop a compressive strengthin 24 hours of at least about 50 psi, at least about 100 psi, at leastabout 500 psi, or more. In some embodiments, the compressive strengthvalues may be determined using destructive or non-destructive methods ata temperature ranging from 100° F. to 200° F.

In some embodiments, the set-delayed cement compositions may havedesirable thickening times after activation. Thickening time typicallyrefers to the time a fluid, such as a set-delayed cement composition,remains in a fluid state capable of being pumped. A number of differentlaboratory techniques may be used to measure thickening time. Apressurized consistometer, operated in accordance with the procedure setforth in the aforementioned API RP Practice 10B-2, may be used tomeasure whether a fluid is in a pumpable fluid state. The thickeningtime may be the time for the treatment fluid to reach 70 Bc and may bereported as the time to reach 70 Bc. In some embodiments, the cementcompositions may have a thickening time of greater than about 1 hour,alternatively, greater than about 2 hours, alternatively greater thanabout 5 hours at 3,000 psi and temperatures in a range of from about 50°F. to about 400° F., alternatively, in a range of from about 80° F. toabout 250° F., and alternatively at a temperature of about 140° F.

Embodiments may include the addition of a cement set activator to theset-delayed cement compositions. Examples of suitable cement setactivators include, but are not limited to: zeolites, amines such astriethanolamine, diethanolamine; silicates such as sodium silicate; zincformate; calcium acetate; Groups IA and IIA hydroxides such as sodiumhydroxide, magnesium hydroxide, and calcium hydroxide; monovalent saltssuch as sodium chloride; divalent salts such as calcium chloride;nanosilica (i.e., silica having a particle size of less than or equal toabout 100 nanometers); polyphosphates; and combinations thereof. In someembodiments, a combination of the polyphosphate and a monovalent saltmay be used for activation. The monovalent salt may be any salt thatdissociates to form a monovalent cation, such as sodium and potassiumsalts. Specific examples of suitable monovalent salts include potassiumsulfate, and sodium sulfate. A variety of different polyphosphates maybe used in combination with the monovalent salt for activation of theset-delayed cement compositions, including polymeric metaphosphatesalts, phosphate salts, and combinations thereof. Specific examples ofpolymeric metaphosphate salts that may be used include sodiumhexametaphosphate, sodium trimetaphosphate, sodium tetrametaphosphate,sodium pentametaphosphate, sodium heptametaphosphate, sodiumoctametaphosphate, and combinations thereof. A specific example of asuitable cement set activator comprises a combination of sodium sulfateand sodium hexametaphosphate. In particular embodiments, the activatormay be provided and added to the set-delayed cement composition as aliquid additive, for example, a liquid additive comprising a monovalentsalt, a polyphosphate, and optionally a dispersant.

Some embodiments may include a cement set activator comprisingnanosilica. As used herein, the term “nanosilica” refers to silicahaving a particle size of less than or equal to about 100 nanometers(“nm”). The size of the nanosilica may be measured using any suitabletechnique. It should be understood that the measured size of thenanosilica may vary based on measurement technique, sample preparation,and sample conditions such as temperature, concentration, etc. Onetechnique for measuring the particle size of the nanosilica isTransmission Electron Microscopy (TEM). An example of a commerciallyavailable product based on laser diffraction is the ZETASIZER Nano ZSparticle size analyzer supplied by Malvern Instruments, Worcerstershire,UK. In some embodiments, the nanosilica may comprise colloidalnanosilica. The nanosilica may be stabilized using any suitabletechnique. In some embodiments, the nanosilica may be stabilized with ametal oxide, such as lithium oxide, sodium oxide, potassium oxide,and/or a combination thereof. Additionally the nanosilica may bestabilized with an amine and/or a metal oxide as mentioned above.Embodiments of the nanosilicas have an additional advantage in that theyhave been known to fill in pore space in cements which can result insuperior mechanical properties in the cement after it has set.

Some embodiments may include a cement set activator comprising acombination of a monovalent salt and a polyphosphate. The monovalentsalt and the polyphosphate may be combined prior to addition to theset-delayed cement composition or may be separately added to theset-delayed cement composition. The monovalent salt may be any salt thatdissociates to form a monovalent cation, such as sodium and potassiumsalts. Specific examples of suitable monovalent salts include potassiumsulfate and sodium sulfate. A variety of different polyphosphates may beused in combination with the monovalent salt for activation of theset-delayed cement compositions, including polymeric metaphosphatesalts, phosphate salts, and combinations thereof, for example. Specificexamples of polymeric metaphosphate salts that may be used includesodium hexametaphosphate, sodium trimetaphosphate, sodiumtetrametaphosphate, sodium pentametaphosphate, sodiumheptametaphosphate, sodium octametaphosphate, and combinations thereof.A specific example of a suitable cement set activator comprises acombination of sodium sulfate and sodium hexametaphosphate.Interestingly, sodium hexametaphosphate is also known in the art to be astrong retarder of Portland cements. Because of the unique chemistry ofpolyphosphates, polyphosphates may be used as a cement set activator forembodiments of the set-delayed cement compositions disclosed herein. Theratio of the monovalent salt to the polyphosphate may range, forexample, from about 5:1 to about 1:25 or from about 1:1 to about 1:10.Embodiments of the cement set activator may comprise the monovalent saltand the polyphosphate salt in a ratio (monovalent salt to polyphosphate)ranging between any of and/or including any of about 5:1, 2:1, about1:1, about 1:2, about 1:5, about 1:10, about 1:20, or about 1:25.

In some embodiments, the combination of the monovalent salt and thepolyphosphate may be mixed with a dispersant and water to form a liquidadditive for activation of a set-delayed cement composition. Examples ofsuitable dispersants include, without limitation, the previouslydescribed dispersants, such as sulfonated-formaldehyde-based dispersantsand polycarboxylated ether dispersants. One example of a suitablesulfonated-formaldehyde-based dispersant is a sulfonated acetoneformaldehyde condensate, available from Halliburton Energy Services,Inc., as CFR-3™ dispersant. One example of a suitable polycarboxylatedether dispersant is Liquiment® 514L or 5581F dispersants, available fromBASF Corporation, Houston, Tex.

The liquid additive may function as a cement set activator. As discussedabove, a cement set activator may also accelerate the setting of theset-delayed or heavily retarded cement. The use of a liquid additive toaccelerate a set-delayed or heavily retarded cement is dependent uponthe compositional makeup of the liquid additive as well as thecompositional makeup of the set-delayed or heavily retarded cement. Withthe benefit of this disclosure, one of ordinary skill in the art shouldbe able to formulate a liquid additive to activate and/or accelerate aset-delayed or heavily retarded cement composition.

The formulation of the liquid additive is a delicate balance thatcorrelates with the specific compositional makeup of the set-delayedcement composition. The amount of the monovalent salt and thepolyphosphate must be carefully balanced in relation to the dispersant.A liquid additive with an irregular mixture of components may lead to aset-delayed cement composition with less than optimal rheology. In someembodiments, the liquid additive may be added to the set-delayed cementcomposition in an amount of from about 1% to about 20% by weight of theset-delayed cement composition and, alternatively, from about 1% toabout 10% by weight of the set-delayed cement composition.

The monovalent salt may be present in the liquid additive in an amountof about 0.1% to about 30% by weight of the liquid additive. In specificembodiments, the polyphosphate may be present in an amount rangingbetween any of and/or including any of about 0.1%, about 1.0%, about10%, or about 30% by weight of the liquid additive. With the benefit ofthis disclosure, one of ordinary skill in the art should be able toformulate a liquid additive with a sufficient amount of polyphosphatefor a specific application.

The polyphosphate may be present in the liquid additive in an amount ofabout 0.1% to about 30% by weight of the liquid additive. In specificembodiments, the polyphosphate may be present in an amount rangingbetween any of and/or including any of about 0.1%, about 1.0%, about10%, or about 30% by weight of the liquid additive. With the benefit ofthis disclosure, one of ordinary skill in the art should be able toformulate a liquid additive with a sufficient amount of polyphosphatefor a specific application.

The dispersant may be present in the liquid additive in an amount ofabout 0.1% to about 90% by weight of the liquid additive. In specificembodiments, the dispersant may be present in an amount ranging betweenany of and/or including any of about 0.1%, about 1%, about 50%, or about90% by weight of the liquid additive. With the benefit of thisdisclosure, one of ordinary skill in the art should be able to formulatea liquid additive with a sufficient amount of dispersant for a specificapplication.

The water may be present in the liquid additive in an amount of about50% to about 90% by weight of the liquid additive. In specificembodiments, the water may be present in an amount ranging between anyof and/or including any of about 50%, about 60%, about 75%, or about 90%by weight of the liquid additive. With the benefit of this disclosure,one of ordinary skill in the art should be able to formulate a liquidadditive with a sufficient amount of water for a specific application.

In accordance with embodiments, the component ratio of the liquidadditive may be relative to the makeup of the set-delayed cementcomposition. Whereby the amounts of the monovalent salt, polyphosphate,and the dispersant are therefore a function of the amounts of the lime,pumice, and sum total of the water (i.e. the water in the set-delayedcement composition and any water in the liquid additive) used in theactivated cement composition.

Without being limited by theory, the main limitations in the formulationof the liquid additive are the solubility limits of the monovalent saltand the polyphosphate; and the amount of dispersant necessary to providethe cement with an acceptable rheology. The solubility limit is innateto the chosen monovalent salt and polyphosphate and therefore notalterable; however, the amount of dispersant is linked to the amounts ofthe monovalent salt and polyphosphate. The amounts of the monovalentsalt/polyphosphate and the dispersant are in a pseudo directrelationship, whereby in a balanced formulation increasing the amount ofone requires an increase in the amount of the other to maintain abalanced composition. For example, if the monovalent salt and thepolyphosphate amounts are increased, the dispersant must also beincreased or the cement composition will be too thick to pump. On thecontrary, if the dispersant amount is increased, the cement compositionwill be too thin and the solid particulates may settle out of solutionunless the amounts of the monovalent salt and the polyphosphate are alsoincreased.

In some embodiments, the liquid additive should provide for a thickeningtime at wellbore conditions of greater than about 1 hour, alternatively,greater than about 2 hours, alternatively greater than about 5 hours. Insome embodiments, the liquid additive may provide a thickening time atwellbore conditions of about four to about six hours. As describedabove, thickening time typically refers to the time a fluid, such as acement composition, remains in a fluid state capable of being pumped.The liquid additive affects the rheology of the cement composition.Therefore, a liquid additive may affect the pump time of a cement. Ifcement rheology is not optimal the activated cement composition may betoo thick or too thin, and therefore would be unsuitable for the desiredpump time.

In some embodiments, the liquid additive may provide a set-delayed orheavily retarded cement with desirable 24-hour mechanical properties.Desirable mechanical properties include 24 hour compressive strengththat is greater than 250 psi, a uniform density (i.e. no settling), andthe absence of any free fluid.

Without being limited by theory, a description of a mechanism foractivation of a lime and pumice set-delayed cement composition using aset-delayed cement activator comprising a combination of sodium sulfateand sodium hexametaphosphate is provided. It is believed that the sodiumsulfate produces sodium hydroxide upon reaction with the lime. Thisreaction causes a resulting rise in the pH of the slurry andconsequently an increase in the rate of dissolution of silicon dioxide.Cement hydration rate has a direct relationship with the proportion offree silicates and/or aluminosilicates. Sodium hexametaphosphatechelates and increases the dissolution rate of calcium hydroxide. Thecombination of sodium sulfate and sodium hexametaphosphate creates asynergy in various compositions of set-delayed cement compositions thatprovides better results than the singular use of either cement setactivator.

The cement set activator may be added to embodiments of the set-delayedcement composition in an amount sufficient to induce the set-delayedcement composition to set into a hardened mass. In certain embodiments,the cement set activator may be added to the set-delayed cementcomposition in an amount in the range of about 0.1% to about 20% byweight of the pumice. In specific embodiments, the cement set activatormay be present in an amount ranging between any of and/or including anyof about 0.1%, about 1%, about 5%, about 10%, about 15%, or about 20% byweight of the pumice. One of ordinary skill in the art, with the benefitof this disclosure, will recognize the appropriate amount of cement setactivator to include for a chosen application.

As will be appreciated by those of ordinary skill in the art,embodiments of the set-delayed cement compositions may be used in avariety of subterranean operations, including primary and remedialcementing. In some embodiments, a set-delayed cement composition may beprovided that comprises water, pumice, hydrated lime, a set retarder,and optionally a dispersant. The set-delayed cement composition may beintroduced into a subterranean formation and allowed to set therein. Asused herein, introducing the set-delayed cement composition into asubterranean formation includes introduction into any portion of thesubterranean formation, including, without limitation, into a wellboredrilled into the subterranean formation, into a near wellbore regionsurrounding the wellbore, or into both. Embodiments may further includeactivation of the set-delayed cement composition. The activation of theset-delayed cement composition may comprise, for example, the additionof a cement set activator to the set-delayed cement composition.

In some embodiments, a set-delayed cement composition may be providedthat comprises water, pumice, hydrated lime, a set retarder, andoptionally a dispersant. The set-delayed cement composition may bestored, for example, in a vessel or other suitable container. Theset-delayed cement composition may be permitted to remain in storage fora desired time period. For example, the set-delayed cement compositionmay remain in storage for a time period of about 1 day or longer. Forexample, the set-delayed cement composition may remain in storage for atime period of about 1 day, about 2 days, about 5 days, about 7 days,about 10 days, about 20 days, about 30 days, about 40 days, about 50days, about 60 days, or longer. In some embodiments, the set-delayedcement composition may remain in storage for a time period in a range offrom about 1 day to about 7 days or longer. Thereafter, the set-delayedcement composition may be activated, for example, by addition of acement set activator, introduced into a subterranean formation, andallowed to set therein.

In primary cementing embodiments, for example, embodiments of theset-delayed cement composition may be introduced into an annular spacebetween a conduit located in a wellbore and the walls of a wellbore(and/or a larger conduit in the wellbore), wherein the wellborepenetrates the subterranean formation. The set-delayed cementcomposition may be allowed to set in the annular space to form anannular sheath of hardened cement. The set-delayed cement compositionmay form a barrier that prevents the migration of fluids in thewellbore. The set-delayed cement composition may also, for example,support the conduit in the wellbore.

In remedial cementing embodiments, a set-delayed cement composition maybe used, for example, in squeeze-cementing operations or in theplacement of cement plugs. By way of example, the set-delayedcomposition may be placed in a wellbore to plug an opening (e.g., a voidor crack) in the formation, in a gravel pack, in the conduit, in thecement sheath, and/or between the cement sheath and the conduit (e.g., amicroannulus).

An embodiment comprises a method of cementing comprising: providing aset-delayed cement composition comprising water, pumice, hydrated lime,and a set retarder; activating the set-delayed cement composition with aliquid additive to produce an activated cement composition, wherein theliquid additive comprises a monovalent salt, a polyphosphate, adispersant, and water; and allowing the activated cement composition toset.

An embodiment comprises an activated cement composition comprising:water; pumice; hydrated lime; a set retarder; a monovalent salt; and apolyphosphate.

An embodiment comprises a cementing system comprising: a set-delayedcement composition comprising: water, pumice, hydrated lime, and a setretarder; and a liquid additive for activation of the set-delayed cementcomposition comprising: water, a monovalent salt, a polyphosphate, and adispersant.

Referring now to FIG. 1, the preparation of a set-delayed cementcomposition in accordance with example embodiments will now bedescribed. FIG. 1 illustrates a system 2 for the preparation of aset-delayed cement composition and subsequent delivery of thecomposition to a wellbore in accordance with certain embodiments. Asshown, the set-delayed cement composition may be mixed in mixingequipment 4, such as a jet mixer, re-circulating mixer, or a batchmixer, for example, and then pumped via pumping equipment 6 to thewellbore. In some embodiments, the mixing equipment 4 and the pumpingequipment 6 may be disposed on one or more cement trucks as will beapparent to those of ordinary skill in the art. In some embodiments, ajet mixer may be used, for example, to continuously mix thelime/settable material with the water as it is being pumped to thewellbore. In set-delayed embodiments, a re-circulating mixer and/or abatch mixer may be used to mix the set-delayed cement composition, andthe activator may be added to the mixer as a powder prior to pumping thecement composition downhole. Additionally, batch mixer type units forthe slurry may be plumbed in line with a separate tank containing acement set activator. The cement set activator may then be fed in-linewith the slurry as it is pumped out of the mixing unit.

An example technique for placing a set-delayed cement composition into asubterranean formation will now be described with reference to FIGS. 2Aand 2B. FIG. 2A illustrates surface equipment 10 that may be used inplacement of a set-delayed cement composition in accordance with certainembodiments. It should be noted that while FIG. 2A generally depicts aland-based operation, those skilled in the art will readily recognizethat the principles described herein are equally applicable to subseaoperations that employ floating or sea-based platforms and rigs, withoutdeparting from the scope of the disclosure. As illustrated by FIG. 2A,the surface equipment 10 may include a cementing unit 12, which mayinclude one or more cement trucks. The cementing unit 12 may includemixing equipment 4 and pumping equipment 6 (e.g., FIG. 1) as will beapparent to those of ordinary skill in the art. The cementing unit 12may pump a set-delayed cement composition 14 through a feed pipe 16 andto a cementing head 18 which conveys the set-delayed cement composition14 downhole.

Turning now to FIG. 2B, the set-delayed cement composition 14 may beplaced into a subterranean formation 20 in accordance with exampleembodiments. As illustrated, a wellbore 22 may be drilled into thesubterranean formation 20. While wellbore 22 is shown extendinggenerally vertically into the subterranean formation 20, the principlesdescribed herein are also applicable to wellbores that extend at anangle through the subterranean formation 20, such as horizontal andslanted wellbores. As illustrated, the wellbore 22 comprises walls 24.In the illustrated embodiment, a surface casing 26 has been insertedinto the wellbore 22. The surface casing 26 may be cemented to the walls24 of the wellbore 22 by cement sheath 28. In the illustratedembodiment, one or more additional conduits (e.g., intermediate casing,production casing, liners, etc.), shown here as casing 30 may also bedisposed in the wellbore 22. As illustrated, there is a wellbore annulus32 formed between the casing 30 and the walls 24 of the wellbore 22and/or the surface casing 26. One or more centralizers 34 may beattached to the casing 30, for example, to centralize the casing 30 inthe wellbore 22 prior to and during the cementing operation.

With continued reference to FIG. 2B, the set-delayed cement composition14 may be pumped down the interior of the casing 30. The set-delayedcement composition 14 may be allowed to flow down the interior of thecasing 30 through the casing shoe 42 at the bottom of the casing 30 andup around the casing 30 into the wellbore annulus 32. The set-delayedcement composition 14 may be allowed to set in the wellbore annulus 32,for example, to form a cement sheath that supports and positions thecasing 30 in the wellbore 22. While not illustrated, other techniquesmay also be utilized for introduction of the set-delayed cementcomposition 14. By way of example, reverse circulation techniques may beused that include introducing the set-delayed cement composition 14 intothe subterranean formation 20 by way of the wellbore annulus 32 insteadof through the casing 30.

As it is introduced, the set-delayed cement composition 14 may displaceother fluids 36, such as drilling fluids and/or spacer fluids that maybe present in the interior of the casing 30 and/or the wellbore annulus32. At least a portion of the displaced fluids 36 may exit the wellboreannulus 32 via a flow line 38 and be deposited, for example, in one ormore retention pits 40 (e.g., a mud pit), as shown on FIG. 2A. Referringagain to FIG. 2B, a bottom plug 44 may be introduced into the wellbore22 ahead of the set-delayed cement composition 14, for example, toseparate the set-delayed cement composition 14 from the fluids 36 thatmay be inside the casing 30 prior to cementing. After the bottom plug 44reaches the landing collar 46, a diaphragm or other suitable deviceshould rupture to allow the set-delayed cement composition 14 throughthe bottom plug 44. In FIG. 2B, the bottom plug 44 is shown on thelanding collar 46. In the illustrated embodiment, a top plug 48 may beintroduced into the wellbore 22 behind the set-delayed cementcomposition 14. The top plug 48 may separate the set-delayed cementcomposition 14 from a displacement fluid 50 and also push theset-delayed cement composition 14 through the bottom plug 44.

The exemplary set-delayed cement compositions disclosed herein maydirectly or indirectly affect one or more components or pieces ofequipment associated with the preparation, delivery, recapture,recycling, reuse, and/or disposal of the disclosed set-delayed cementcompositions. For example, the disclosed set-delayed cement compositionsmay directly or indirectly affect one or more mixers, related mixingequipment, mud pits, storage facilities or units, compositionseparators, heat exchangers, sensors, gauges, pumps, compressors, andthe like used generate, store, monitor, regulate, and/or recondition theexemplary set-delayed cement compositions. The disclosed set-delayedcement compositions may also directly or indirectly affect any transportor delivery equipment used to convey the set-delayed cement compositionsto a well site or downhole such as, for example, any transport vessels,conduits, pipelines, trucks, tubulars, and/or pipes used tocompositionally move the set-delayed cement compositions from onelocation to another, any pumps, compressors, or motors (e.g., topside ordownhole) used to drive the set-delayed cement compositions into motion,any valves or related joints used to regulate the pressure or flow rateof the set-delayed cement compositions, and any sensors (i.e., pressureand temperature), gauges, and/or combinations thereof, and the like. Thedisclosed set-delayed cement compositions may also directly orindirectly affect the various downhole equipment and tools that may comeinto contact with the set-delayed cement compositions such as, but notlimited to, wellbore casing, wellbore liner, completion string, insertstrings, drill string, coiled tubing, slickline, wireline, drill pipe,drill collars, mud motors, downhole motors and/or pumps, cement pumps,surface-mounted motors and/or pumps, centralizers, turbolizers,scratchers, floats (e.g., shoes, collars, valves, etc.), logging toolsand related telemetry equipment, actuators (e.g., electromechanicaldevices, hydromechanical devices, etc.), sliding sleeves, productionsleeves, plugs, screens, filters, flow control devices (e.g., inflowcontrol devices, autonomous inflow control devices, outflow controldevices, etc.), couplings (e.g., electro-hydraulic wet connect, dryconnect, inductive coupler, etc.), control lines (e.g., electrical,fiber optic, hydraulic, etc.), surveillance lines, drill bits andreamers, sensors or distributed sensors, downhole heat exchangers,valves and corresponding actuation devices, tool seals, packers, cementplugs, bridge plugs, and other wellbore isolation devices, orcomponents, and the like.

To facilitate a better understanding of the present embodiments, thefollowing examples of certain aspects of some embodiments are given. Inno way should the following examples be read to limit, or define, theentire scope of the embodiments.

EXAMPLES Example 1

The following example describes an example liquid additive compositionfor use with an example set-delayed cement composition. For thisexample, the liquid additive was added to the set delayed cementcomposition in the amount of 8% of the total mass of the combinedhydrated lime and pumice. After activation, the activated set-delayedcement composition had a thickening time of 5.5 hours at 100° F. Thethickening time was measuring using a pressurized consistometer at 100°F. in accordance with the procedure for determining cement thickeningtimes set forth in API RP Practice 10B-2, Recommended Practice forTesting Well Cements, First Edition, July 2005. As discussed above,varying the concentration of the dispersant without adjusting themonovalent salt and polyphosphate to compensate may produce an activatedslurry with less than optimal rheology and may alter the thickeningtime.

The example set-delayed cement composition comprised water; DS-325lightweight aggregate pumice, available from Hess Pumice Products, Inc.,Malad, Id.; hydrated lime; Liquiment 5581F® dispersant, available fromBASF Corporation, Houston, Tex.; and Micro Matrix® cement retarder(MMCR), available from Halliburton Energy Services, Inc., Duncan, Okla.The compositional makeup is presented in Table 1 below. The amountslisted in Table 1 are shown as a percentage by weight of the pumice.

TABLE 1 Example Set-Delayed Cement Composition Component % by weight ofpumice Water 60 Pumice 100 Hydrated Lime 20 Dispersant 0.7 Retarder 1.26

The example liquid additive comprised water, a monovalent (sodiumsulfate), a polyphosphate (sodium hexametaphosphate), and Liquiment5581F® dispersant. The compositional makeup is presented in Table 2below. The amounts listed are shown as a percentage of the totalcomposition of the liquid additive.

TABLE 2 Example Liquid Additive Weight % of Liquid Component AdditiveWater 68.7 Monovalent Salt 13.7 Polyphosphate 13.7 Dispersant 3.4

Example 2

In this example, a series of six liquid additive samples were preparedfor use with an example set-delayed cement composition. The compositionfor the set-delayed cement composition is presented in Table 3 below. InTable 3, “% bwP” stands for “percentage by weight of pumice” and“gal/sk” stands for “gallons per sack 46 lb. sack of pumice.” The liquidadditive comprised water, a monovalent salt (sodium sulfate), apolyphosphate (sodium hexametaphosphate), and Liquiment 5581F®dispersant. The water, monovalent salt, and polyphosphate amounts wereheld constant as shown in Table 4 below. The dispersant concentrationwas varied each of the six samples as shown in Table 5 below. The liquidadditive from Table 4 was added to the set-delayed cement compositionfrom Table 3 such that the liquid additive comprised 10% of the combinedweight of the set-delayed cement composition and the liquid additive.

TABLE 3 Example Set-Delayed Cement Composition Component Amount UnitsWater 64.1 % bwP Pumice 100 % bwP Hydrated Lime 19.8 % bwP Coatex 1.8 %bwP MMCR 0.06 gal/sk MicroMax 2.06 % bwP HR-5 0.516 % bwP

TABLE 4 Example Liquid Additive Wt % of total sum of the water,monovalent salt, and the Component polyphosphate Water 83.33 MonovalentSalt 8.33 Polyphosphate 8.33 Dispersant X

The dispersant amounts varied from a range of 0.00% to 4.3%. Therheology of the slurries also varied based on the amount of dispersantpresent since the monovalent salt and polyphosphate amounts were heldconstant. To reiterate, the dispersant amount is a percentage of thetotal activated composition. After preparation, the rheologicalproperties of the samples were determined using a Model 35A FannViscometer and a No. 2 spring with a Fann Yield Stress Adapter, inaccordance with the procedure set forth in API RP Practice 10B-2,Recommended Practice for Testing Well Cements. The data is presented inTable 5 below. The rheological data shown in Table 5 are apparentviscosity values measured at a hear rate of 100 (1/sec).

TABLE 5 Dispersant Amount vs. Rheology Sample # Dispersant AmountRheology in centipoise 1 0.00 2704 2 0.45 754 3 0.68 468 4 0.90 390 52.4 286 6 4.3 260

Example 2 illustrates that varying the dispersant amount, withoutcompensating by adjusting the monovalent salt and the polyphosphateamounts, may create slurries with less than optimal rheologies.

Slurry Sample 1 from Table 5 was unworkable and was not pourable.Archimedes tests were performed for the remaining 5 slurries. In orderto do the Archimedes tests, each of the samples was poured into 2″×4″cylinders and left to set at 140° F. for 24 hours. The set samples werethen cut into three equally spaced parts along the length of thecylinders. Using the Archimedes principle of density and displacement,the densities of the samples were determined and recorded in units oflb/gal. The results are presented in Table 6 below.

TABLE 6 Sample Density Measurements Sample # Top Middle Bottom 1 N/A N/AN/A 2 11.71 11.78 11.84 3 12.11 12.14 12.18 4 12.3 12.3 12.4 5 12.1912.19 12.20 6 12.06 12.3 12.7

Samples 2-5 had no significant settling issues. Sample 6 did displaysettling. In general, the more dispersant that is added, the lessviscous the cement slurry will be. Sample 5 possessed the best slurrycharacteristics and would be the optimal choice compared to the other 5samples on this measure alone. The other slurries could potentially beoptimal when such factors as cost and early mechanical strengthdevelopment are taken into account.

Example 3

The slurry composition presented in Table 3 above was used as an exampleset-delayed cement composition. The example liquid additive formulation,however, is different from the one presented in Table 4. Table 7 lists anew liquid additive formulation specific to this example.

TABLE 7 Example Liquid Additive Wt % of total sum of the water,monovalent salt, and the Component polyphosphate Water 87.5 MonovalentSalt 6.25 Polyphosphate 6.25 Dispersant X

Table 8 depicts the different values for the dispersant described inTable 7. Four different dispersant amounts were used. The dispersantconcentration is a percentage of the total weight of the activatedslurry. The dispersant amount ranged from 0.0% to 4.3%. Afterpreparation, the rheological properties of the samples were determinedusing a Model 35A Fann Viscometer and a No. 2 spring with a Fann YieldStress Adapter, in accordance with the procedure set forth in API RPPractice 10B-2, Recommended Practice for Testing Well Cements. The datais presented in Table 8 below. The rheological data shown in Table 8 areapparent viscosity values measured at a shear rate of 100 (1/sec).

TABLE 8 Dispersant Amount vs. Rheology Sample # Dispersant AmountRheology in centipoise 7 0.00 1274 8 0.45 416 9 0.68 312 10 4.3 234

Archimedes tests were performed for the 4 slurry samples. In order to dothe Archimedes tests, each of the samples was cut into three equallyspaced parts. Using the Archimedes principle of density anddisplacement, the densities of the samples were determined and recordedin units of lb/gal. The results are presented in Table 9 below.

TABLE 9 Densities of Samples Described in Table 8 Sample # Top MiddleBottom 7 11.80 11.80 11.86 8 12.04 12.06 12.06 9 12.15 12.19 12.31 1011.7 12.2 12.8

Significant settling occurred in Samples 9 and 10, representing 0.68%and 4.3% dispersant respectively. In comparison with Example 2, thisindicates that reducing the amount of liquid additive added to thesample may also cause the optimum liquid additive dispersantconcentration to change. Here the optimum concentration was 0.45%dispersant, whereas in the previous example the optimum concentrationwas 2.4%.

Example 4

In this example, the slurry described in Table 3 was used for the basecomposition. The liquid additive formulation is described in Table 10below. The monovalent salt was sodium sulfate. The polyphosphate wassodium hexametaphosphate. The dispersant was Coatex 1702, available fromCoatex Inc., Chester, S.C. As illustrated in Table 11, the dispersantconcentration varied from 0.45% to 8.33%.

TABLE 10 Example Liquid Additive Wt % of total sum of the water,monovalent salt, and the Component polyphosphate Water 76.9 MonovalentSalt 11.5 Polyphosphate 11.5 Dispersant X

TABLE 11 Dispersant Concentration per Sample Sample Dispersant Wt % oftotal sum of the water, Number Amount (g) monovalent salt, and thepolyphosphate 1 5 0.45 2 15 1.35 3 30 2.65 4 70 5.98 5 100 8.33

In order to determine the effect of varying the dispersant concentrationon the compressive strength of set samples, the compressive strength ofeach sample was measured after five days. The destructive compressivestrength was measured by allowing the samples to cure in a 2″ by 4″plastic cylinder that was placed in a water bath at 190° F. to form setcylinders. Immediately after removal from the water bath, destructivecompressive strengths were determined using a mechanical press inaccordance with API RP 10B-2, Recommended Practice for Testing WellCements. The results of this test are set forth below in Table 12, inunits of psi. The reported compressive strengths are an average for twocylinders of each sample.

TABLE 12 Compressive Strength Tests Sample Number Compressive Strength(psi) 1 964 2 778 3 398 4 411 5 34

Varying the dispersant concentration had a direct impact on thecompressive strength of the samples. This effect was stronger than thesettling effect of adding dispersant. It therefore stands to reason thatthe dispersant can have an antagonistic effect on the sodiumhexametaphosphate activation of the extended life slurry when retardedwith the phosphonate, nitrilotrismethylenetriphosphonic acid.

Archimedes tests were performed for Samples 1-5. Each of the samples waspoured into 2″×4″ cylinders and left to set at 140° F. for five days.The set samples were then cut into three equally spaced parts along thelength of the cylinders. Using the Archimedes principle of density anddisplacement, the densities of the samples were determined and recorded.The results are presented in Tables 13-17 below, where PPG is the symbolfor units of lb/gal.

TABLE 13 Sample 1 Archimedes Test Volume (mL) Weight (g) Density (g/mL)Density (PPG) Top 65.96 99.18 1.5036 12.5 Middle 60.55 91.12 1.5049 12.5Bottom 64.29 96.45 1.5002 12.5

TABLE 14 Sample 2 Archimedes Test Volume (mL) Weight (g) Density (g/mL)Density (PPG) Top 54.31 81.58 1.5021 12.5 Middle 67.38 100.97 1.498512.5 Bottom 54.18 81.53 1.5048 12.5

TABLE 15 Sample 3 Archimedes Test Volume (mL) Weight (g) Density (g/mL)Density (PPG) Top 60.56 90.98 1.5023 12.5 Middle 57.44 85.84 1.4944 12.4Bottom 61.3 91.8 1.4976 12.5

TABLE 16 Sample 4 Archimedes Test Volume (mL) Weight (g) Density (g/mL)Density (PPG) Top 60.63 89.53 1.4767 12.3 Middle 58.83 87.83 1.4929 12.4Bottom 62.12 93.05 1.4979 12.5

TABLE 17 Sample 5 Archimedes Test Volume (mL) Weight (g) Density (g/mL)Density (PPG) Top 64.04 94.09 1.4692 12.2 Middle 56.47 82.6 1.4627 12.2Bottom 59.5 87.91 1.4775 12.3

Samples 4 and 5 displayed slight settling behavior.

Example 5

In this example, ten sample liquid additives were prepared for use witha set-delayed cement composition. The compositional makeup of theset-delayed cement composition is presented in Table 18 below. Theliquid additive comprised water, a monovalent salt in the form of sodiumsulfate, a polyphosphate in the form of sodium hexametaphosphate, andLiquiment 5581F® dispersant. It should be noted that the percentages ofthe monovalent salt and the polyphosphate were held constant throughoutthe experiment while the dispersant concentration was varied. Thecomposition of the liquid additive is illustrated below in Table 19. Allof the listed amounts are shown as a percentage of the total compositionof the liquid additive. The liquid additive from Table 19 was added tothe set-delayed cement composition described in Table 18 such that themonovalent salt and polyphosphate were present in the combined amount of1.25 bwP or 1.00% bwP.

TABLE 18 Example Set-Delayed Cement Composition Component Amount unitsWater 60.0 % bwP Pumice 100.0 % bwP Hydrated Lime 20 % bwP Liquiment5581F 0.6 % bwP MMCR 0.06 gal/sk MicroMax 2.0 % bwP HR-5 0.5 % bwPSA-1015 0.035 % bwP

TABLE 19 Example Liquid Additive Wt % of total sum of the water,monovalent Component salt, and the polyphosphate Water 81.59  MonovalentSalt 8.53 Polyphosphate 8.53 Dispersant X

The dispersant amount varied from a range of 0.10% to 1.39%. Thethickening time of the slurries varied based on the amount ofdispersant, since the monovalent salt and polyphosphate were heldconstant.

The compressive strength and thickening times of each sample weremeasured. The destructive compressive strength was measured by allowingthe samples to cure in a 2″ by 4″ plastic cylinder that was placed in awater bath at 190° F. to form set cylinders. Immediately after removalfrom the water bath, destructive compressive strengths were determinedusing a mechanical press in accordance with API RP 10B-2, RecommendedPractice for Testing Well Cements. The results of this test are setforth in Table 20 below. The reported compressive strengths are anaverage for three cylinders of each sample.

TABLE 20 Dispersant Amount vs. Thickening Time and Compressive StrengthMonvalent Salt and Dispersant Thickening Sample Polyphosphate AmountTime Compressive Number Amount (% bwP) (% bwP) (hr:min) Strength (psi) 11.25 0.10 1:59 1047 2 1.25 0.23 2:18 — 3 1.25 0.49 2:54 — 4 1.25 0.883:51 741 5 1.25 1.15 4:07 824 6 1.25 1.41 4:53 1146 7 1.00 0.08 2:461201 8 1.00 0.87 4:44 1066 9 1.00 1.13 4:48 635 10 1.00 1.39 11:17  672

Varying the dispersant concentration of the liquid additive allowed thethickening time of the set-delayed cement composition to be controlled.This added benefit was realized through the observation that thethickening time of the cement samples increased with increasingdispersant amount. For the liquid additive samples containing 1.25% bwPmonovalent salt-polyphosphate, the relationship is almost linear asshown in FIG. 3.

It should be understood that the compositions and methods are describedin terms of “comprising,” “containing,” or “including” variouscomponents or steps, the compositions and methods can also “consistessentially of” or “consist of” the various components and steps.Moreover, the indefinite articles “a” or “an,” as used in the claims,are defined herein to mean one or more than one of the element that itintroduces.

For the sake of brevity, only certain ranges are explicitly disclosedherein. However, ranges from any lower limit may be combined with anyupper limit to recite a range not explicitly recited, as well as, rangesfrom any lower limit may be combined with any other lower limit torecite a range not explicitly recited, in the same way, ranges from anyupper limit may be combined with any other upper limit to recite a rangenot explicitly recited. Additionally, whenever a numerical range with alower limit and an upper limit is disclosed, any number and any includedrange falling within the range are specifically disclosed. Inparticular, every range of values (of the form, “from about a to aboutb,” or, equivalently, “from approximately a to b,” or, equivalently,“from approximately a-b”) disclosed herein is to be understood to setforth every number and range encompassed within the broader range ofvalues even if not explicitly recited. Thus, every point or individualvalue may serve as its own lower or upper limit combined with any otherpoint or individual value or any other lower or upper limit, to recite arange not explicitly recited.

Therefore, the present embodiments are well adapted to attain the endsand advantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent embodiments may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Although individual embodiments arediscussed, all combinations of each embodiment are contemplated andcovered by the disclosure. Furthermore, no limitations are intended tothe details of construction or design herein shown, other than asdescribed in the claims below. Also, the terms in the claims have theirplain, ordinary meaning unless otherwise explicitly and clearly definedby the patentee. It is therefore evident that the particularillustrative embodiments disclosed above may be altered or modified andall such variations are considered within the scope and spirit of thepresent disclosure. If there is any conflict in the usages of a word orteen in this specification and one or more patent(s) or other documentsthat may be incorporated herein by reference, the definitions that areconsistent with this specification should be adopted.

What is claimed is:
 1. A method of cementing comprising: providing aset-delayed cement composition comprising water, pumice, hydrated lime,and a set retarder; activating the set-delayed cement composition with aliquid additive to produce an activated cement composition, wherein theliquid additive comprises a monovalent salt, a polyphosphate, adispersant, and water; and allowing the activated cement composition toset.
 2. The method of claim 1 wherein the liquid additive is added tothe set-delayed cement composition in an amount of about 1% to about 20%by weight of the set-delayed cement composition.
 3. The method of claim1 wherein the monovalent salt is present in the liquid additive in anamount of about 0.1% to about 30% by weight of the liquid additive,wherein the polyphosphate is present in the liquid additive in an amountof about 0.1% to about 30% by weight of the liquid additive, wherein thedispersant is present in the liquid additive in an amount of about 0.1%to about 90% by weight of the liquid additive, and wherein the water ispresent in the liquid additive in an amount of about 50% to about 90% byweight of the liquid additive.
 4. The method of claim 1 wherein thepolyphosphate comprises sodium hexametaphosphate.
 5. The method of claim1 wherein the monovalent salt comprises sodium sulfate.
 6. The method ofclaim 1 wherein the dispersant comprises a polycarboxylated ether. 7.The method of claim 1 wherein the ratio of the monovalent salt to thepolyphosphate is from about 5:1 to about 1:25.
 8. The method of claim 1wherein the polyphosphate comprises sodium hexametaphosphate, themonovalent salt comprises sodium sulfate, and the dispersant comprises apolycarboxylated ether.
 9. The method of claim 1 wherein the set-delayedcement composition remains in a pumpable fluid state for a time periodof about 4 hours to about 6 hours after activation.
 10. The method ofclaim 1 further comprising storing the set-delayed cement compositionfor a period of about 1 day or longer.
 11. The method of claim 1 furthercomprising introducing the activated cement composition into asubterranean formation.
 12. The method of claim 1 further comprisingpumping the activated cement composition through a conduit, through acasing shoe, and into a wellbore annulus.
 13. A method of cementingcomprising: providing a set-delayed cement composition comprising:water, pumice, hydrated lime, and a set retarder; and providing a liquidadditive for activation of the set-delayed cement compositioncomprising: water, a monovalent salt, a polyphosphate, a dispersant; andallowing the set-delayed cement composition to remain in a storagevessel for about one day or more; activating the set-delayed cementcomposition with the liquid additive to produce an activated cementcomposition by combining the liquid additive with the set delayed cementcomposition in mixing equipment; pumping the activated cementcomposition through a conduit into a wellbore; allowing the activatedcement composition to set.
 14. The cementing method of claim 13 whereinthe polyphosphate comprises sodium hexametaphosphate, the monovalentsalt comprises sodium sulfate, and the dispersant comprises apolycarboxylated ether.